194 MORPHOLOGY OF THE ORGANS OF VERTEBRATES. 



ends of the pronephros, from which they return the blood to the 

 heart. With the development of the mesonephros they extend 

 farther back until they reach the posterior limits of the abdomi- 

 nal cavity. Each gives off intersegmental veins to bring back 

 a portion of the blood sent into the abdominal walls by the 

 intercostal and lumbar arteries, while in the early stages the 



VI 



vit 



VIII 



FIG. 205. Development of the venous system of selachians, after Rabl am 

 Hochstetter. C, caudal; CS, cardinal sinus; J, jugular; LO, left omphalomes 

 araic; P, portal; PC, postcardinal ; RO, right omphalomesaraic ; 5, sinus venosus : 

 SI, subintestinal ; V, vitelline (in V and VII, cloacal loop). Compare VII am 

 VIII with Fig. 206. 



veins from both extremities (subclavians and hypogastrics' 

 empty into the same vessels. 



These post cardinals gradually develop a rich vascular plexu; 

 in the mesonephros, receiving the blood brought from the tail b] 

 the caudal vein, which runs forward between the two Wolffiai 

 bodies. When this system is established the connection betweei 



